1. Field of the Invention
The present invention relates to a demultiplexer, and a light emitting display using the demultiplexer and a display panel thereof. More specifically, the present invention relates to an organic light emitting diode (OLED) display.
2. Discussion of the Related Art
Generally, OLED displays emit light by electrically exciting an organic compound. Such an OLED display includes N×M organic light emitting cells arranged in the form of a matrix, and displays an image by driving the organic light emitting cells, using voltage or current. Such organic light emitting cells are also called “OLEDs” because they have diode characteristics. As shown in FIG. 1, each organic light emitting cell has a structure including an anode electrode layer (e.g., ITO), an organic thin film, and a cathode electrode layer (e.g., metal). The organic thin film has a multi-layer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL), to achieve an improved balance between electrons and holes, and thus, to achieve an enhancement in light emitting efficiency. The organic thin film also includes an electron injecting layer (EIL) and a hole injecting layer (HIL). Such organic light emitting cells are arranged in the form of an N×M matrix to form an OLED display panel.
For driving methods for such an OLED display panel, there are a passive matrix type driving method and an active matrix type driving method using thin film transistors (TFTs). In accordance with the passive matrix type driving method, anodes and cathodes are arranged to be orthogonal to each other so that a desired line to be driven is selected. In accordance with the active matrix type driving method, thin film transistors are coupled to respective indium tin oxide (ITO) pixel electrodes in an OLED display panel so that the OLED display panel is driven by a voltage maintained by the capacitance of a capacitor coupled to the gate of each thin film transistor.
FIG. 1 is a block diagram of a conventional OLED display.
As shown in FIG. 1, the conventional OLED display includes a display panel 10 including a plurality of pixels 11, a scan driver 20, a data driver 30, and switches SW1 to SWm.
The scan driver 20 sequentially transmits a selection signal to a plurality of scan lines S1 to Sn, and the data driver 30 sequentially outputs control signals X1 to Xm for turning on the switches SW1 to SWm.
The switches SW1 to SWm form a demultiplexer for demultiplexing an image signal transmitted from an image signal line and for transmitting the image signal to data lines D1 to Dm, and sequentially transmit the image signal to the data lines D1 to Dm in response to the control signals X1 to Xm.
In the conventional OLED display, the data driver 30 is required to have output terminals corresponding to the data lines, and to sequentially apply the image signal to the respective data lines D1 to Dm for a horizontal period. Therefore, it is limited to programming the image signal to one data line at a time.
To provide more time for programming each data line, multiple data lines should be driven at the same time by dividing and transmitting the image signal to a plurality of signal lines, and turning on the plurality of switches at the same time when a signal (e.g., signal X1) is applied by a data driver.
However, when one signal output from the data driver 30 is transmitted to a plurality of switches, a time for a control signal X being transmitted to the plurality of switches has a variation. Accordingly, an image signal is not correctly transmitted to the data lines D1 to Dm.